Process for production of phosphoric acid



AMay 31, 1927. 1,630,283

w. H. WAGGAMAN Er Al. I

PROCESS FORv PRODUCTION 0E PHOSPHORIC ACID it. f Y" Hem/jy W Ialrwoad,

2 l May 31,1927. wr H'WAGGAMAN ET AL 1,630, 83

PROCESS FOR PRODUCTION OF PHOSPHORIC ACID Filed Jan. 2s. '1924 2- sheets-sheet 2 Wlam ff Wag 0172072, Wa@ r11/00d.

UNIT-Eo.STATES 'l "P'atiaed MayA s1 WILLIAM n. WAGGAMA'N AND-HENRY w.

NoIs, .luisI'cfN-oasA 'ro vieron CHEMICAL Appucationn'lea gaius/ry as' 1924. serial ms.' carpal.

This invention relates to a new and useful.

. process `'for' the manufacture of phosphoric acid by' the volatilization process, and relates -m'ore particularly to a process adapted 4forl the production of phosphorus and phosphoric acid by the vvolatiliz'ation process from either 'lump or briquetted charges of natural phosphates, silica and coke. `It has for? its object. the bringingabout of lthe necl0v essary chemical reactions more expeditiously and economically than has;heretofore been accomplished.v A further object ofthis invention is to maintain throughout the major part of the furnace or kiln, with the least expenditure of fuel,A a teni erature Sulliciently high to bring 'about the evolution4 ofl phosphorus` from thefurnacc. charge. It is'` an object toprovide a process whereby the desired reducing conditionsmay be ma-n- ,tained throughout the necessary portion'of` Other and further objects wilifbppear as the description proceeds. L

It has heretofore been proposedito produce l phosphoric acid from mixturesof phosphate rock, silica and coke, orother reducing agent, by heating'such` mixtures in furnaces of various types', including `the' ele tric arc furnace, shaft furnaces of the blast urnace type wherein fueLis used as a 'heating source, andin rotary vkilns of the type ordinarily employedv in 'the 4manufacture of cemen .The present invention, however, relates to methods of operating shaft kilns hayingin penditure of fuel.

While a temperature sutlicient to bring about reactions between mixtures of phosfs hate rock, silica and coke,.can be attained 1n the lower portion of --an ordinary'lilne ij kiln, the lnature ofthe charge employed 1s combination therewith certain novel features` such that the high teni erature zone 'cannot extend to any great hexghtw'ithin the 'Unlike a blast furnace as a rule,.these kilns mazo PIATENrL oF-Fics.

Easrnnwoon, o r cHIcAjoo mamme, ILLI- wonxs, or ca rcaeo, rumors, nl'oondo no operate under heavy air p'ressure and theref rethe quantity of air drawn in near the base is `rather liinitedi The burnin of 'the -fuel in' the lower portions of the illn therefore soon uses up' this air and as t e gases proceed up thefshaft in contact with [hot coke, they become so depleted in oxygen that combustion. soon ceases. Moreover, the

' reduction of the phosphoric acid in the natural' phosphates to'elemental phosphorus isa highly en'dothermic reaction, entailiiig the, `absorption Lof so muchY heat perature of. the upper part o Jthe 'kiln isl at the tembrought below the point at which this realetion will take place.

While themalntenance of reducing conditions is essential to bringA about the elimination of phosphorus from charges of phospahate rbck, silica and coke,- at temperatures kr nging from 1200 to 1500 C., it ishiglily l desirable toV regenerate and return to the systenri the major part of the heat absorbed under 'these reducing conditions.' Where phosphoricacid,`and not elemental phos- ,plorus is the product ,'sought,l this return o plished byburning the evolved4 phosphorus almost as s oon as It isset free, by introducing into, thev kiln at various points up .they

heat to the system can be readily accomshaft vregulated supplies of auxiliary air`orf oxidizinggases.

'have not been operate" successfully with the hosphate charge, is, that heretofore .it has een` commonly supposed that the ratio of silica to lime in charges suitable for the hosphoricacid, must such as to give a usible slag. Unless the temperature of such charges is raised to a point where the slag obtained is quite molten,'"sem1fu`sed masses lcomplete or nearly. compleete volatilizationf Another reason? wh ordinary'lime kilnsv are obtained which tend to clogthe shaft,

interfering with the regular. operation thereand in kilns of the type'ord'narily em- 'ployed in burning lime it is vdiiiicult to maintain slag .in such a du We have .'found, hmweve1-',I that-it is not essential to vhave present. anamount of silica id condition.

insuch charges which willgive a fusible f slag wllen the massois heated to il temperal ture as high as 1450? C., and have been' able condition.-`

In our-cendin a lication, Serial No. I

P g Pl?3 `686;891, liledjanuary 1 1924, we have de -A scribed abriquetted charge consisting of an intimate mixture of finely ground natural phosphate, silica land coke or other solid reducing agent, wherein the ratiolof 'lime to silica is somewhat greater than that in calcium ortho silicate tCa2SiO4) in which-the' ratio of' lime to silica is 1.86 to'l. The fusf ing point ofsuch mixtures not only is higher than the temperature which 'should be \ob taine in the shaft kiln, but also considrably bove that necessary tobring about ay reaction wherein-the' phosphorus is volatilized. hi'le. we prefer to7 use a briquetted charge ofthe type mentioned above, mixed ywith lmnp coke for fuel purposes, we vdo no t wish to be limited to the use of briquettes, since-under certain conditions, the various ingredients may also' be employedin large fragments dr lump form?.

In' carrying'out this invention, we propose` "to em loy a kilnof thev shaft type, .several modi cationsrof which areillust-rated'in the, accompanying drawings. The main-.prin ciplg employed, however, in all of thesemo'diiieatlons is essentially.. the same, `and consists 'in introducing at` various heights along the shaft, limited quantities of air or .35 oxidizing gases to -augment that drawn in at the base of the kiln. The quantity of' auxil, iary airfint'roducedmt these points may beso regulated as to l'irfrgonly the elemental phosphorus or phosphorus.. and carbon' -Jmonoxide freed by the reducing reactions in the l'zones immediatelr below said inlets.

The quantity' 'of-V air admitted;v however, I

should beflimited, Vso as. to burnl only1 -aminimum amount ofl the solid fuel which is a part ofthe-.furnace pharge and which. i's burned chieflfy7 by the ain admittebdt the base of theklln. l

In case it isdeSirabIe', however, tQ burn coke or other solid` fuel alasoat the p ointsI of entrance ofthe auxiliaryair, in order to increase still further the temperature of the' system, a somewhat modified form of this shaft kiln may be em loyed wherein pi'o vision' is made. for feeding additional eokeor 'will desend close to the inner walls thereof, and form a more or lessprotective layer-y around the phosphatecharge. protecting it,

'7 solid fuel to the kiln in such a Way that it proper temperat1'1re,[z 1-` further modification of 'this shaft kiln may be employed. wherein provision is made for feeding coke or other the lower end thereof.

We have illustrated in the accompanying solid reducing agent into't-he shaft close to drawings, certain preferred embodiments ot",

apparatus adapted for carrying out our process. A

In'fthe .drawings- Figure 1 is Ha vertical section through one type of furnace; y Figure 2 is a transverse section line 2-2 of Figure 1;

Figure 3 is a view\similar nto Figure 1, but showing a modified. form of construction; and Figure 4' is'a view similar to Figur/e 3 showing a further modified forni.'

talten on Referring vfirst to the form of construction shown in Figures land 2, the substautiallv cylindrical furnace. 11 comprises the metal' shell 12 having brick lining 13. The grate i 14 is located inthe lower end of the furnace and suppprts the charge. The ashes are removed through openings l5. The materials of the charge `comprising phosphate rock,l

silica and a reducing agent suchas coke,- are Introduced,attheglpper end of thefurnace through the hopper 16, the flow being controlled by the bell 17. The flue 18 is provided. at the upper end of the furnace for withdrawing the gaseonsproducts of the 5 process.'

f A plurality of tuyi'es or air inlets 19, 20, 21 and 22` are provided at points spaced rertically of the furnace.l These tn vres are are each controlled b v a valve and are fed ffromthe headers 23, 24. 25' and 26.

Thev form of ,construction.shown in Figurel 3\'comprises a frusto-c-onical furnace v3 which is larger 'at 4its lower `cud. Material is fed at the upper end by hopper 32 controlled byv bell 33, and the gaseous products of combustion'are carriedoff through tlueifl-L The. furnace gs provided with the grate and '.as'h discharge openings 36." It is provided` also, 'with the vertically spaced series of tuyres 37, 38, 39 and 40.. The lower portion of the furnace is provided with'a pllh rality of circumfrentially spaced' hoppers 41, each of which `are providedwith a cov- Y The. formy of-constructidn shown in Figure 4. comprises the frusto-conicalf furnace 51 having the grate52 and as h discharge9 o` enings 53. Thefurnace is provided with t e vertically spaced series of tuyres-54, 55,

56 andf?. Atits upper end` `it is provided with the centrally disposed hopp-er 58, closed -by cover 59. The flue '60 leads from the hopper `r58. The-circumferentially extend-` ing hopper 61 surrounds the hop er A58 and its upper side Lis -elsed by a p urality o f doors62. lthe operation-of Vthe form of furnace shown in Figures 1 and 2 the mixed charge comprising coke or other reducing agent., together with the desired portions of phosphate rock and silica is introduced through the hopper' 16, its introduction being controlled by raising and lowering the bell 1T. The .greater portion'of the air necessary 'for carrying on the combustion, enters the lower portion of the 'furnace through the grac bars 14. As has been stated, how-ever, this air is not sufficient to .cause the necessary combustion to properly heat. the upper portion ot the furnace. Consequently controlled amounts of air, are introduced through the spaced series ot tuyres 1S). :20,- 21 and 22. The amount of air introduced through each series of tuyres or through each tuyere may be controlled so as to providea close control of they ten'iperature and ot' the reducing action throughout the height of the furnace. Suliicient4 air may be introduced to burn only the free phosphorus or enough may be introduced to burn part ot' the At'uel charge.

In the form of construction shown in Figure 3. the mixed charge. is intrmluced at the top in the manner just described. However, the combustion in the upper portions ot'- the furnace, due tov the air introduced through the tuyres,` may be such as'to largely burn the coke before it reaches the 'lower portionI of the furnace. Therefore, 'additional coke is introduced at. the lower portion of the t'urnace through the hopper-s 41. The amount of this coke may be regulated so as to pro'- vide the exact amount necessary for coinbustion at that point.

The form of construction shown inFieul'e 4 is operated in a manner similar to tios-e forms already described. The mixture ot' phosphate rock, silica and fuel is introduced through hopper 58. This mixture is. how-l ever, enclosed in aV protective layer ot' cole.` which is introduced through the circumt'er.. ential hopper 6l. This coke works down adjacent the sides of the furnace and furnishes fuel for combustion with the air introduced through the tuyercs. The coke'mixed with the phosphate rock and silica of the charge acts as a reducing agent with the charge.

We have illustrated three different forms of furnaces adapted -for carrying out, our process, but it is to be understood that it may be carried out with other forms of fur-4 naces. lVe, therefore, contemplate such changes in construction and operation aS con-ie within the spirit and scope of the t'ollowing claims.

lVe claim:

l. The process for thc production ot' phosphoric acid which Acomprises heating by means of solid tuel an extended mass of mixed ljiliospliate rock. silica and coke, in-` troducing oxidizing' gases at. one end of said -mass to burn said fuel and introducing additional oxidizing gases ata plurality of points alonfr said' mas.; to oxidirf.` the phosphorus eyolved'by the reactions between the constituents of thechargc.4

2. The. process -'for the production of phos;y

phoric acid which comprises heat-ing by means of solid "fuel a vertically extending mass ot mixed phosphate rock, silica and coke, and maintaining an approximately uniform temperature throughout the height ot' the mass byintroducing at spaced points along said height. regulated quantities of oxidizing' gases, said gases burning with the phosphorus and carbon monoxide evolved b v reactions in the lower portions of the mass. y

4. The process for thc production of phosphoric acid.. which comprises lheating by means ot. solid fuel a verticallyV extending mass of mixed phosphate rock.y silica and coke, and maintaining an approximately uniform temperature throughout the height of the'fmaes by surrounding said mass with a layer of additional coke and introducing into said layer ot. 'coke at vertically spaced points, additional oxidizing gases.

19th day of January, 1924.

. Signed at Chicago Heights, illinois. this- 

